The present invention relates to an emulation device comprising an emulation unit having a debugging function and a probe having a function to emulate at least a part of functions of a target system. More specifically, the present invention relates to an improvement of such an emulation device that has an analog circuit in the probe.
Emulation devices of the type described are used for an application system with a microcomputer that is to be designated as a target system to debug hardware and software of the target system under the control of a control device. The emulation device comprises an emulation unit and a probe. The probe has a relatively long cable assembly for use in connecting it to the emulation unit. The cable assembly is provided with a probe connector at an end thereof. The probe connector has an integrated circuit for use in emulating peripheral functions of the microcomputer. This integrated circuit is called a peripheral evaluation chip and has digital and analog circuits. The peripheral evaluation chip is connected to the emulation unit and the target system via a power supply line and a ground line contained in the cable assembly.
The emulation unit comprises a plurality of integrated circuits (ICs) such as large-scale integrated circuits (LSIs). The emulation unit is thus affected by instantaneous change in an internal signal in ICs as well as by the impedance of the power supply line and the ground line. As a result, power supply noise may be generated on the power supply line and the ground line. In addition, the cable assembly may serve as an antenna because it is relatively long. This may cause electro-magnetically induced noise on the cable assembly. Such power supply noise or electro-magnetically induced noise affects the peripheral evaluation chip through the power supply line and the ground line. If it happens, the analog circuit contained in the peripheral evaluation chip may be operated in a wrong or false manner.